It is known to use rubber gels, including modified rubber gels, in mixtures with a wide range of rubbers, for example to improve rolling resistance in the manufacture of motor vehicle tyres (see, for example, DE 42 20 563, GB-PS 10 78 400 EP 405 216 and EP 854 171).
Dispersions of silicone-containing graft polymers in liquid amides, which are also prepared from aqueous lattices, are known from DE-A-3742180. However, in the case of the dispersions described in said document, the water is only substantially separated off, and complete separation is difficult.
Compositions containing microgels and organic media have basically been described in non-anticipatory international application PCT/EP2004/052290 of the present applicant.
The inventors of the present invention have found that it is possible finely to disperse microgels, in particular in liquid functional additives, for example using a homogeniser. The division of the microgels into the primary particle range is, for example, a prerequisite for rendering the nano-characteristics of the microgels particularly useful. The compositions according to the invention containing the specific microgels can open up a large number of microgel applications that were not previously accessible using the microgels themselves.
The microgel/additive combinations have highly beneficial characteristics, for example rheology, consistency, shear stability, thickening effect, etc. The inventors were thus able to prepare combinations of conventional commercial liquid lubricant additives and microgels that, in combination, incorporate positive characteristics of both systems. It has thus been found that a liquid additive is bound by the microgel at the surface or in the network and can be introduced in bound form into a lubricant, for example, from where it is also released again under specific conditions. Surprisingly, it has been found not only that additives allow paste- or fat-like combinations to be obtained, but also that these combinations in fact develop synergistic effects. A transparent “additive fat” having consistency values (dripping temperature, penetration) typical of fats, in contrast to opaque fat structures, is thus obtained, for example, from the combination of a sulphur-functionalised olefin and a microgel. If this additive fat is introduced into base fluids in conventional concentrations, a lubricant formulation that behaves synergistically with respect to the measured values determined for the individual components, additive or microgel, is obtained. Further combinations of sulphur-containing additives or phosphorus-containing additives display a similar, usually paste-like consistency, in some cases a fat-like consistency.
The present invention therefore provides a composition containing at least one microgel (B) and at least one functional additive (C).
Microgels (B)
The microgel (B) used in the composition according to the invention is a crosslinked microgel. In a preferred embodiment, the microgel is not crosslinked by high-energy radiation. The term “high-energy” radiation expediently refers, in this context, to electromagnetic radiation having a wavelength of less than 0.1 μm. The use of microgels crosslinked by high-energy radiation, as described for example in Chinese Journal of Polymer Science, Vol. 20, No. 2, (2002), 93-98, is disadvantageous, as it is virtually impossible to prepare on an industrial scale microgels crosslinked by high-energy radiation. The use of high-energy radiation from radioactive sources such as radioactive cobalt is also associated with serious safety problems.
In a preferred embodiment of the invention, the primary particles of the microgel (B) have an approximately spherical geometry. According to DIN 53206:1992-08, the microgel particles, which may be recognised as individual entities using suitable physical methods (electron microscope) and are dispersed in the coherent phase, are designated as primary particles (cf., for example, Römpp Lexikon, Lacke and Druckfarben, Georg Thieme Verlag, 1998). The term an “approximately spherical” geometry means that, on viewing the composition, for example using an electron microscope, the dispersed primary particles of the microgels may be seen to have a substantially circular surface. Since the microgels do not substantially change their form or morphology during processing of the compositions according to the invention, the foregoing and following remarks similarly also apply to the microgel-containing compositions obtained using the composition according to the invention such as, for example, plastics materials, coating agents, lubricants or the like.
In the primary particles of the microgel (B) that are contained in the composition according to the invention, the deviation in the diameter of an individual particle, defined[(d1−d2)/d2]×100,wherein d1 and d2 are two arbitrary diameters of the primary particle and d1>d2, is preferably less than 250%, more preferably less than 100%, even more preferably less than 80%, even more preferably less than 50%.
Preferably at least 80%, more preferably at least 90%, even more preferably at least 95% of the primary particles of the microgel exhibit a diameter deviation, defined as[(d1−d2)/d2]×100,wherein d1 and d2 are two arbitrary diameters of the primary particle and d1>d2, of lees than 250%, preferably less than 100%, more preferably less than 80%, even more preferably less than 50%.
The above-mentioned deviation in the diameters of the individual particles can be determined by the following method. First of all, a thin section of the compacted composition according to the invention is prepared. A transmission electron micrograph enlarged by a factor of, for example, 10,000 or 200,000 is then prepared. In an area of 833.7×828.8 nm, the largest and the smallest diameter of 10 microgel primary particles are determined as d1 and d2. If the above-defined deviation is in each case less than 250%, preferably less than 100%, even more preferably less than 80%, even more preferably less than 50%, in at least 80%, preferably at least 90%, more preferably at least 95% of the measured microgel primary particles, the microgel primary particles exhibit the above-defined feature of deviation.
If the concehtration of the microgels in the composition is sufficiently high that the visible microgel primary particles are markedly superimposed, evaluation may be facilitated by appropriate prior dilution of the test sample.
In the composition according to the invention, the primary particles of the microgel (B) preferably exhibit an average particle diameter from 5 to 500 nm, more preferably from 20 to 400 nm, more preferably from 20 to 300 nm, more preferably from 20 to 250 nm, even more preferably from 20 to 99, even more preferably from 40 to 80 (diameters to DIN 53206). The preparation of particularly finely divided microgels by emulsion polymerisation takes place by controlling the reaction parameters in a manner known per se (see, for example, H. G. Elias, Makromoleküle, Vol. 2, Technologie, fifth edition, page 99 ff.).
Since the morphology of the microgels basically does not change during further processing of the composition according to the invention, the average particle diameter of the dispersed primary particles substantially corresponds to the average particle diameter of the dispersed primary particles, in the products of further processing obtained using the composition according to the invention such as microgel-containing plastics materials, lubricants, coatings, etc. This is a particular advantage of the composition according to the invention. Customers may in some cases be provided with tailor-made, liquid microgel formulations, which are stable in storage, have a defined microgel morphology and may easily be processed by customers in the desired applications. Complex prior dispersion, homogenisation or even preparation of microgels is no longer required, so it is expected that microgels of this type will also be used in fields in which their use previously seemed excessively complex.
In the composition according to the invention, the microgels (B) expediently comprise fractions which are insoluble in toluene at 23° C. (gel content) of at least approximately 70% by weight, more preferably at least approximately 80% by weight, even more preferably at least 90% by weight.
The fraction that is insoluble in toluene is determined in toluene at 23° C. 250 mg of the microgel are steeped in 20 ml toluene for 24 hours at 23° C. while shaking. After centrifugation at 20,000 rpm, the insoluble fraction is separated and dried. The gel content is determined from the quotient of the dried residue and the weighed portion and is given as a percentage by weight.
In the composition according to the invention, the microgels (B) expediently exhibit a swelling index of less than approximately 80, more preferably of less than 60, even more preferably of less than 40 in toluene at 23° C. The swelling indices of the microgels (Qi) may thus particularly preferably be between 1-15 and 1-10. The swelling index is calculated from the weight of the solvent-containing microgel steeped in toluene for 24 hours at 23° C. (after centrifugation at 20,000 rpm) and the weight of the dry microgel:
Qi=Wet weight of the microgel/dry weight of the microgel.
In order to determine the swelling index, 250 mg of the microgel is steeped in 25 ml toluene for 24 hours while shaking. The gel is centrifuged off, weighed and then dried at 70° C. until a constant weight is reached and dried again.
In the composition according to the invention, the microgels (B) expediently exhibit glass transition temperatures Tg from −100° C. to +120° C., more preferably from −100° C. to +100° C., even more preferably from −80° C. to +80° C. In rare cases, microgels which, owing to their high degree of crosslinking, do not exhibit a glass transition temperature may also be used.
Moreover, the microgels (B) used in the composition according to the invention preferably exhibit a glass transition temperature range greater than 5° C., preferably greater than 10° C., more preferably greater than 20° C. Microgels that exhibit such a glass transition temperature range, in contrast to completely homogeneously radiation-crosslinked microgels, are generally not completely homogenised. As a result, the change in modulus from the matrix phase to the dispersed phase is not direct in the microgel-containing plastics material compositions prepared, for example, from the compositions according to the invention. Accordingly, in the event of these compositions being subjected to abrupt stress, there are no tearing effects between the matrix and the dispersed phase, so the mechanical characteristics, the swelling behaviour and the stress corrosion cracking, etc. are advantageously influenced.
The glass transition temperatures (Tg) and the glass transition temperature range (ΔTg) of the microgels are determined by differential scanning calorimetry (DSC). under the following conditions: Two cooling/heating cycles are carried out for determining Tg and ΔTg. Tg and ΔTg are determined in the second heating cycle. In order to determine these values, 10-12 mg of the selected microgel are placed in a Perkin-Elmer DSC sample container (standard aluminium pan). The first DSC cycle is carried out by first cooling the sample with liquid nitrogen to −100° C. and then heating it at a rate of 20 K/min to +150° C. The second DSC cycle is started by immediate cooling of the sample as soon as a sample temperature of +150° C. has been reached. The cooling takes place at a rate of approximately 320 K/min. In the second heating cycle, as in the first cycle, the sample is heated once again to +150° C. The heating rate in the second cycle is again 20 K/min. Tg and ΔTg are determined graphically on the DSC curve of the second heating process. For this purpose, three straight lines are plotted on the DSC curve. The first straight line is plotted on the curved portion of the DSC curve below Tg, the second straight line on the branch of the curve extending through Tg with a turning point and the third straight line on the branch of the DSC curve above Tg. Three straight lines with two intersections are thus obtained. Each intersection is characterised by a characteristic temperature. The glass transition temperature Tg is obtained as an average value of these two temperatures and the glass transition temperature range ΔTg is obtained from the difference between the two temperatures.
The microgels that are contained in the composition according to the invention and are preferably not crosslinked by high-energy radiation may be prepared in a manner known per se (see, for example, EP-A-405 216, EP-A-854 171, DE-A 4220563, GB-PS 1078400, DE 197 01 489.5, DE 197 01 488.7, DE 198 34 804.5, DE 198 34 803.7, DE 198 34 802.9, DE 199 29 347.3, DE 199 39 865.8, DE 199 42 620.1, DE 199 42 614.7, DE 100 21 070.8, DE 100 38 488.9, DE 100 39 749.2, DE 100 52 287.4, DE 100 56 311.2 and DE 100 61 174.5). Patents (applications) EP-A-405 216, DE-A 4220563 and GB-PS 1078400 claim the use of CR, BR and NBR microgels in mixtures with double bond-containing rubbers. DE 197 01 489.5 discloses the use of subsequently modified microgels in mixtures with double bond-containing rubbers such as NR, SBR and BR.
The term “microgels” expediently refers to rubber particles obtained, in particular, by crosslinking the following rubbers:    BR: polybutadiene,    ABR: butadiene/acrylic acid/C1-4 alkylester copolymers,    IR: polyisoprene,    SBR: styrene/butadiene copolymers having styrene contents from 1-60, preferably 5-50 per cent by weight,    X-SBR: carboxylated styrene/butadiene copolymers    FKM: fluorine rubber,    ACM: acrylate rubber,    NBR: polybutadiene/acrylonitrile copolymers having acrylonitrile contents from 5-60, preferably 10-50 per cent by weight,    X-NBR: carboxylated nitrile rubbers    CR: polychloroprene    IIR: isobutylene/isoprene copolymers having isoprene contents from 0.5-10 per cent by weight,    BIIR: brominated isobutylene/isoprene copolymers having bromine contents from 0.1-10 per cent by weight,    CIIR: chlorinated isobutylene/isoprene copolymers having bromine contents from 0.1-10 per cent by weight,    HNBR: partially and completely hydrogenated nitrile rubbers    EPDM: ethylene/propylene/diene copolymers,    EAM: ethylene/acrylate copolymers,    EVM: ethylene/vinyl acetate copolymers    CO and ECO: epichlorohydrin rubbers,    Q: silicone rubbers, except silicone graft polymers,    AU: polyester urethane polymers,    EU: polyether urethane polymers    ENR: epoxidised natural rubber or mixtures thereof.